Dear Doctors: I am a 47-year-old woman in good health. I exercise regularly and eat a healthy diet. At my physical, I was surprised when my doctor said I have A-fib. I have never felt anything wrong with my heart, so I am confused. Can you please explain A-fib?

Dear Reader: You are asking about a heart condition called atrial fibrillation. Often referred to simply as A-fib, it is a type of heart arrhythmia. The heartbeat we rely on to circulate blood throughout the body is made up of a precise series of rhythmic contractions. This includes the timing of the heartbeats, and the slight pause between them. If any element of this series goes awry for even a short period of time, it is known as an arrhythmia.

To better understand, we should start with a bit of anatomy. A healthy adult heart is roughly the size of a clenched fist and resembles an inverted pear. It is divided into four chambers, two above and two below. The lower chambers are known as the left and right ventricles. The two on top, which are the ones involved in the arrhythmia you have been diagnosed with, are called the left and right atrium.

The right atrium and right ventricle work together to receive the blood that has just traveled throughout the body and move it into the lungs. There, it gets topped off with oxygen. The left atrium and left ventricle work together to receive the now-oxygen-rich blood exiting the lungs and to send it off to the tissues of the body.

When someone has atrial fibrillation, it means the two upper chambers of the heart have ceased to function properly. It occurs due to a malfunction in a cluster of cells in the right atrium, known as the sinus node, which send out the electrical signals that regulate heart rhythm.

Rather than producing the strong and coordinated contractions needed to move blood through the heart valves and into the ventricles, the atria behave erratically. This can include beating too fast, making quivering and incomplete contractions, failing to pause between contractions and beating out of sync with the ventricles below. The result is a chaotic heartbeat that stalls the flow of blood through the heart. It can cause blood to pool in the atria, which can clot. This, in turn, raises the risk of a stroke. In 15% to 20% of strokes, A-fib is a factor.

As has happened with you, not everyone with A-fib develops symptoms. When they do manifest, symptoms can include a fast and irregular pulse, a fluttery sensation in the chest, general fatigue, unusual fatigue when exercising, shortness of breath, dizziness and weakness. Reduced blood flow in the heart can cause angina, which is chest pain or a sensation of pressure.

The fact you are not experiencing symptoms does not mean this diagnosis can be ignored. Treatment typically includes identifying the reason for the condition, reducing stroke risk and using medications or appropriate procedures to restore normal heart rhythm. It would be wise for you to follow up this diagnosis with a cardiologist.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: Like a lot of people, I’ve had to return to the office. At home, I did calls and meetings on the treadmill, walked at lunch and lifted weights during breaks. That’s not possible now. I know sitting is bad for your health. Can you discuss the research? I’d like to share it with my boss.

Dear Reader: Whether you work at a desk, enjoy leisure activities from a couch or mainly use a car to get from one place to another, modern Americans spend more time sitting than at any point in history. For many, the total is well over 10 hours of sitting per day. That’s the number that research associates with a marked increase in cardiac risk. And for bodies built for motion, this shift has proven to be a significant threat to health.

These long stretches of sitting play a significant role in weight gain, obesity, loss of lean muscle mass, rising body fat percentage, increases in abdominal fat, hypertension and poor blood glucose control. These, in turn, translate into an increased risk of developing diabetes, a wide range of cardiovascular diseases, cancers and early death.

Mental health takes a hit as well. A sedentary lifestyle is associated with an increased risk of anxiety, depression and changes to cognition. Small wonder that the prolonged inactivity that marks modern life has come to be referred to as “sitting disease.”

The newest study into the potential health dangers of being sedentary comes from researchers in Australia. Interested in whether prolonged sitting might be associated with an early death, they analyzed 14 years of health data gathered from 5,836 middle-aged adults. They found the risk of death from any cause was 47% higher among people who were sedentary than those who were active.

We are happy to be able to balance this sobering news with research looking at the question from the other perspective. That is, the positive effects on physical health of being active. A study in the British Journal of Sports Medicine analyzed the health outcomes of 44,300 women and men whose lifestyles ranged from completely sedentary to moderately active. The researchers found that even brief sessions of daily exercise helped ease the adverse effects of prolonged sitting. However, the greatest benefit came from doing 35 minutes of exercise at moderate intensity per day. Interestingly, additional research shows this doesn’t have to occur all in a single session, but can be broken up into smaller increments if needed.

In another interesting study, researchers at the University of Chicago found that using a small exercise device located under their desks can be beneficial for seated workers. Known as a HOVR, it’s basically a leg swing that keeps the person’s lower body in motion. Workers using the HOVR burned almost 20% more calories than those who sat still, and 7% more calories than those at standing desks.

In an era where 80% of jobs are sedentary, finding ways to be active at work is critical to good health. We hope sharing this information with your boss will prove helpful.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: My husband and I both work in an office, and our three kids are in school. That’s a lot of exposure to germs and bugs. When someone gets sick, how do you know if it’s a cold or the flu -- or worse? Do you always need to see a doctor?

Dear Reader: A variety of viruses, bacteria and even fungi can cause respiratory tract infections. Because they affect the same tissues, they often produce similar symptoms. That can make it difficult to know which illness someone has contracted.

The most common respiratory infections here in the United States are two that you’re asking about, namely the flu, or influenza, and the common cold. Other possibilities include COVID-19, pneumonia and bronchitis. Unlike during the height of the pandemic, the flu is outpacing COVID-19 this year. Pneumonia, another possible respiratory infection, is not as common as the flu or a cold. (We are addressing COVID-19 and pneumonia in upcoming columns. Our recent column about bronchitis can be found in the archives.)

The common cold is caused by a virus, usually rhinovirus and sometimes coronavirus. An identifying characteristic of a plain old cold is that the symptoms it causes occur from the neck up. These include a sore throat, clogged sinuses, a runny nose, sneezing, the production of thick (and seemingly endless) mucus, ear congestion, watery eyes and sometimes a headache. Mild chest congestion and a mild fever are possible, but do not always occur.

Having a cold can be miserable, but it rarely needs medical intervention. One notable exception is if it generates an ear infection. This can occur if bacteria begin to grow in fluid that has built up in the middle ear. Symptoms of an ear infection include pain, muffled hearing, visible discharge and dizziness. If symptoms persist or become severe, it can become necessary to see a doctor for antibiotics to clear up the infection.

That brings us to the flu, which is caused by the influenza virus. Unlike a cold, which typically has a gradual onset, the flu hits hard and fast. Symptoms can be similar to those of the common cold, but are markedly more intense. People with the flu often have a high fever; chills, exhaustion and widespread body aches are common. The infection can also affect the respiratory tract, causing a persistent cough and mucus production.

For both a cold and the flu, recovery begins with rest and supportive care. The symptoms are caused by your immune system’s fight against the viral invaders, so you want to help it along. That means drinking plenty of fluids, eating a healthy diet and -- yes, we’re repeating ourselves here -- getting plenty of rest. Over-the-counter medications to address fever, cough, sore throat and congestion can be helpful. Most people will begin to recover in three to five days. For those with influenza, the antiviral medication Tamiflu is an option.

Many people ride out these illnesses at home. But if symptoms become severe, consider an office visit with your doctor for evaluation, diagnosis and further treatment.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)